1. Field of the Invention
The present invention relates to a rest apparatus movably guided and provided with a pair of rest shoes which contact and support a cylindrical workpiece to be machined.
2. Description of the Prior Art
In a conventional rest apparatus for a grinding machine, as shown in FIG. 1, a rest housing 3 having an upper shoe 1 and a lower shoe 2 is movably guided by a pair of horizontally parallel pilot shafts 4. The axes of the pilot shafts 4 are located at a position lower than the axis of a workpiece to be ground, so that the rest housing 3 receives a clockwise moment, as viewed in FIG. 1, by a grinding resistance exerted on the upper shoe 1 by a grinding wheel, not shown. The rest housing 3 also receives a counterclockwise moment, as viewed in FIG. 1, by the action of the lower shoe 2 supporting the weight of the workpiece.
Since the lower shoe 2 supports the weight of the workpiece, a substantially constant force is applied to the lower shoe 2. On the other hand, the upper shoe 1 supports a grinding resistance which is varied depending upon the grinding condition, that is, either a rough or fine grinding operation. Therefore, when the direction of the resultant moment caused by the upper and lower shoes 1 and 2 is reversed, the rest housing 3 is fluctuated, resulting in the lowering of the rigidity of the rest apparatus. In particular, the grinding resistance is lowered at the fine grinding operation, so that the rotary moment on the rest housing is reversed in direction when the grinding operation is changed from rough to fine, with the result of possible vibration mark on the workpiece being ground.